The present invention pertains to rotary valves, that is to valves in which a rotatable closure element is mounted in a flowway defined by the valve body so that it may be rotated between its open and closed positions. Examples of such valves are butterfly or disc valves, ball valves, plug valves, and the like. The valve body of such an assembly, which defines the fluid flowway, particularly in the case of a butterfly or disc valve, is typically provided with an annular seat or seal engageable with the periphery of the disc to seal against fluid leakage when the valve is closed. While, in some cases, such valve seats may be formed of elastomeric and/or polymeric materials, there are situations in which it is preferred to use a metallic seat or seal, e.g. because of the chemical and/or thermal environment in which the valve is to be used. In any event, such a seat must generally project slightly radially inwardly into the flowway when the valve is open so that, as the valve is closed, the seat will be expanded radially outwardly by the disc to form a tight seal therewith. Additionally, and perhaps even more importantly, when the valve is closed, the disc tends to travel in the axial direction when the pressure increases, and it is important that the seat also accommodate this movement while maintaining a fluid seal. If the valve element and the valve body undergo thermal expansion at different rates, the seat should be capable of accommodating the relative movement caused by such expansion. The seat must also be provided with "memory" so that, when the valve is reopened, the seat will assume its original position so that it will again form a tight seal the next time the valve is closed.
Metallic valve seats typically have some spring characteristics which tend to provide the aforementioned memory. However, in most instances, it is necessary to supplement these inherent properties of the seat. In the past, springs have been employed for this purpose. For example, a coil spring might be disposed in generally surrounding relation to the seat, or the sealing portion thereof, to provide memory.
Such prior devices suffer from several disadvantages. For example, when used at elevated temperatures, the conventional spring will lose spring temper and cease to properly perform its function of providing memory for the valve seat. Attempts to overcome these disadvantages, while still employing conventional springs, merely result in further complication of the device and undue expense.